BISMARCK, N.D. — Two more suspects have pleaded guilty in a Jamaican lottery scam that authorities say cost dozens of mostly elderly Americans millions of dollars.

The pleas by Jason Jahalal and Xanu Morgan in late September came as federal prosecutors in North Dakota continue efforts to reach deals with the 13 suspects who have been arrested and brought to the U.S. to face charges. The suspects are accused of calling victims about bogus lottery winnings, persuading them to send advance fees to receive the purported winnings, then keeping the money without paying out anything to the victims.

Six of the 15 defendants in the case have now reached agreements calling for them to plead guilty to conspiracy, with the government dropping fraud and money laundering counts and recommending that they pay restitution. Three of the six have pleaded guilty, two more are scheduled to do so later this month, and a sixth was to plead Tuesday but the hearing was called off so attorneys can fine-tune his agreement. Seven suspects remain scheduled for trial in January, and two more remain fugitives.

Jamaican lottery scams have been happening for years, but prosecutors say this is believed to be the first large-scale scam prosecuted in the U.S. Authorities allege it bilked at least 90 Americans out of more than $5.7 million. Prosecutors began building their case after a North Dakota woman lost her life savings of more than $300,000 in 2011.

Lavrick Willocks, the man accused of being the scam’s kingpin, pleaded guilty in late July. His sentencing hasn’t been scheduled. Prosecutors are recommending a sentence of about 10 years in prison.